Every time I've visited Bubba Gumps on City Walk it's been a straight walk-in, no waiting around. That said, if you're turning up at 19:30 with a party of 10 people then its going to be more tricky.

You can't book in advance, but the place is a lot bigger than you think. Also, unlike many of the other spots on City Walk you don't get priority if staying at a Universal Orlando hotel which is a shame.